Julien Pouysegur

Sub-100-fs Yb:CALGO nonlinear regenerative amplifier

We report on the first diode-pumped Yb:CaGdAlO4 regenerative amplifier in the sub-100-fs regime. It generates pulses at a central wavelength of 1047 nm with up to 24 μJ energy (after compression) at a repetition rate of 50 kHz. The measured pulse duration is 97 fs, with a spectral bandwidth of 19 nm. We describe in detail how nonlinear effects are optimally used to compensate gain narrowing in order to overcome the 100 fs barrier.

Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier.

Active coherent beam combination using a 7-non-coupled core, polarization maintaining, air-clad, Yb-doped fiber is demonstrated as a monolithic and compact power-scaling concept for ultrafast fiber lasers. A microlens array matched to the multicore fiber and an active phase controller composed of a spatial light modulator applying a stochastic parallel gradient descent algorithm are utilized to perform coherent combining in the tiled aperture geometry. The mitigation of nonlinear effects at a pulse energy of 8.9 µJ and duration of 860 fs is experimentally verified at a repetition rate of 100 kHz. The experimental combining efficiency results in a far field central lobe carrying 49% of the total power, compared to an ideal value of 76%. This efficiency is primarily limited by group delay differences between cores which is identified as the main drawback of the system. Minimizing these group delay issues, e.g. by using short and straight rod-type multicore fibers, should allow a practical power scaling solution for femtosecond fiber systems.

Numerical and Experimental Analysis of Nonlinear Regenerative Amplifiers Overcoming the Gain Bandwidth Limitation

We present a numerical and experimental analysis of a nonlinear architecture to overcome the gain bandwidth limitation in regenerative amplifiers. This technique is based on the optimization of dispersion and nonlinear effects during the amplification process to obtain broad-bandwidth pulses that can be compressed to short durations with high temporal quality. We demonstrate the advantage of this method to maintain an excellent temporal quality of pulses even at high levels of optical nonlinearity. The technique has been applied to regenerative amplifiers using Yb:YAG, Yb:KYW, and Yb:CALGO crystals as gain media. In all cases we achieved the shortest pulse duration ever obtained from regenerative amplifiers using the respective laser crystals. These results underline the benefits of this amplification technique with respect to current state of the art.

Hybrid high-energy high-power pulsewidth-tunable picosecond source.

A hybrid ytterbium-doped fiber-bulk laser source allowing the generation of 3 ps, 350 μJ, 116 MW peak power Fourier transform-limited pulses at 50 kHz repetition rate and 1030 nm wavelength is described. Pulse duration tunability is provided by an adjustable spectral compression-based seeder system. Energy scaling capabilities of the architecture by use of the divided-pulse amplification method are investigated. This source provides a robust, compact, and versatile solution for applications such as RF photocathode guns, x- and γ-ray generation by inverse Compton scattering, and optical parametric chirped-pulse amplification pumping.

Simple Yb:YAG femtosecond booster amplifier using divided-pulse amplification

A hybrid-system approach using a low-gain Yb:YAG single crystal booster amplifier behind a state-of-the-art industrial high-power femtosecond fiber system is studied to significantly increase the output pulse energy of the fiber amplifier. With this system, more than 60 W of average power is demonstrated at 100 kHz for pulse duration of 400 fs, corresponding to an energy per pulse of 600 µJ. Reducing the repetition rate, the energy is increased up to 2.5 mJ (before compression), which corresponds to the limitation due to laser damage threshold of the optical coatings. To scale further the energy, passive divided-pulse amplification is then implemented at the entrance of the bulk amplifier. Using this geometry, a safe nominal operating point is presented with output pulse energies of 3 mJ before and 2.3 mJ after compression and with a pulse duration of 520 fs, corresponding to a peak power of 4.4 GW.

Generation of 150-fs pulses from a diode-pumped Yb:KYW nonlinear regenerative amplifier

Generation of sub-150-fs-level pulses has been obtained from an Yb-doped crystal-based regenerative amplifier by applying an innovative amplification scheme. This scheme is based on optimization of the linear and non-linear phase during the amplification process inside the regenerative amplifier cavity. This technique with Yb:KYW allows to achieve pulse durations from diode-pumped Yb-doped regenerative amplifiers that were up to now only accessible with more complex Ti:sapphire amplifiers. With this Yb-doped tungstate crystal used in regenerative amplifiers, 145 fs pulses centered at 1026 nm with a spectral bandwidth of 14 nm at 50 kHz for an average power of 1.6 W have been generated.

Single-stage Yb:YAG booster amplifier producing 2.3 mJ, 520 fs pulses at 10 kHz

520fs, 2.3-mJ pulses are demonstrated in a Yb:YAG booster amplifier delivering peak powers up to 4.4GW. To avoid damage and nonlinear-effect issues, passive divided pulse amplification is studied for the first time for bulk-amplifier.

Generation of sub-100-fs pulses in an Yb: CaGdAlO4 regenerative amplifier by tailored control of linear and nonlinear phase

Generation of sub 100 fs pulse has been obtained in an Yb:CALGO regenerative amplifier using nonlinear effects. It exhibits 97fs pulses at 1047nm with up to 24μJ energy with a spectral bandwidth of 19nm.

Generation of sub-100 fs pulses in a Yb:CALGO regenerative amplifier

Ultra short pulse down to 100 fs has been obtained in a regenerative amplifier using Yb doped CALGO crystals. By employment of nonlinearity we succeed to overcome gain narrowing limitation.